1. Field of the Invention
The present invention relates to a bumper structure for a motor vehicle, particularly to the bumper structure with an impact absorber arranged between a bumper reinforcement and a bumper fascia for reducing impact energy applied to a pedestrian involved in a collision with a motor vehicle.
2. Description of the Related Art
A bumper structure for a motor vehicle of this kind is disclosed in, for example, Japanese patent laying-open publication Tokkai 2002-144988, particularly shown in its FIGS. 2 and 5. This bumper structure is constituted of a bumper reinforcement, also called as a bumper armature or a bumper beam, attached to a front end portion of a vehicular body, a bumper fascia located in front of the bumper reinforcement, and an impact absorption member arranged between the bumper reinforcement and the bumper fascia.
The bumper reinforcement extends in a lateral direction of the vehicular body and has a stepped or tapered front surface, in cross-section, such that its upper portion retreats in a longitudinal direction of the vehicular body with respect to its lower portion. The impact absorption member has a flat front surface to be fitted to an inner side of the bumper fascia, and a stepped or tapered rear surface, in cross-section, to mate with the front surface of the bumper reinforcement such that its upper portion retreats rearward in the longitudinal direction with respect to its lower portion. This results in the impact absorption member is constructed so that its lower portion is shorter in the longitudinal direction than is its upper portion.
In this conventional bumper structure, when a motor vehicle collides with a pedestrian, impact force is applies to legs of the pedestrian and the bumper structure. By the impact force, the impact absorption member is pressed and deformed in the longitudinal direction while absorbing impact energy and thereby decreases damage to legs of the pedestrian. Specially, during this collision, upper and lower portions of the impact absorption member are deformed to absorb the impact energy, and amounts of their compressive deformations are different from each other, because the lower portion is formed smaller in the longitudinal direction than the upper portion. This results in the upper portion being deformed to retreat backward of the vehicular body to a greater extent than the lower portion, which prevents knees of the pedestrian from being bent toward a direction opposite to their natural bending direction, and broken. The impact absorption member, therefore, reduces damage to a pedestrian's lower legs to a minimum.
The above known conventional bumper structure, however, encounters a problem in that because the upper portion and the lower portion, smaller in the longitudinal direction than the upper portion, of the impact absorption member are different from each other in terms of maximum amounts of compressive deformations, the maximum (limit) deformation amount of the lower portion is attained earlier and is smaller than that for the upper portion, thereby causing lower legs of a pedestrian during a collision with a motor vehicle to encounter much damage such as bone fracture and the like.
It is, therefore, an object of the present invention to provide a bumper structure for a motor vehicle which overcomes the foregoing drawbacks and can prevent a pedestrian from being caught under the motor vehicle, and improve protection of the pedestrian, during a collision with the motor vehicle, against damage to his or her legs, particularly lower legs and knees, such as knee-bending against their natural bending direction, bone fracture of the lower legs and the like.